Exploring liquid fuel combustion dynamics in a swirl burner using dynamic mode decomposition

Aero gas turbine engine combustors are transitioning from traditional Rich-Quench-Lean (RQL) staging to Lean Premixed Prevaporized (LPP) operation to reduce harmful NOx emissions and improve combustion efficiency. This operational shift, however, introduces the risk of thermoacoustic instabilities, a significant concern for reliable operation and integrity of the jet fuel fired aero gas turbines. Moreover, the complex geometries of aero engine combustors and the challenges of partially premixed conditions further complicate stability analysis and demand advanced diagnostic techniques. To that end, this work aims to analyse thermoacoustic and swirl burner instabilities of our in-house designed Magister burner under engine representative lean conditions using Detached Eddy Simulation. We extended our prior analysis by applying Dynamic Mode Decomposition (DMD) in a distributed computing environment, leveraging our PARAMOUNT modal analysis package, to capture the burner's critical acoustic and transient dynamics. The proposed novel DMD combined spectrum effectively identified the mechanism driving vortex core rotation, capturing its frequency to within (Formula presented.) of the measured value. It was demonstrated that using Proper Orthogonal Decomposition (POD) modes directly is more effective than an exact DMD formulation, yielding a (Formula presented.) reduction in the Mean Absolute Error (MAE) of DMD predicted temperature values. Furthermore, the application of variable stacking reduced the MAE of the short-term DMD temperature predictions by (Formula presented.). Finally, an MRDMD adjustment is proposed that leverages a critical Strouhal number (St = 0.6) to significantly enhance ROM by ensuring essential flow dynamics are retained. This novel analysis framework demonstrates a powerful capability to assess thermoacoustic stability, extracting critical physical insights from complex simulations that produce large datasets and thereby accelerating the design cycle for aero-engine combustors.